Abstract: In order to achieve clean coal-fired units emission requirements，the conventional semi-dry desulfurization process for circulating fluidized bed is upgraded，so as to achieve a high desulfurization efficiency, low emission concentration of dust,stable and reliable operation，and so on.This process is particularly suitable for burning low-sulfur coal unit.Compared the dominate process by wet desulfurization,the upgraded of semi-dry desulfurization process is cheaper by investment and higher efficiency by comprehensive benefits.This paper is taking an example of a thermal power plant in Zhejiang, full-depth analysising the whole project transformation process from the absorption tower, bag filter and the control system.Adoption of the operational data determining , the semi-dry process route not only can meet the current stringent clean emission requirements, but also has more advantages than the wet desulfurization .In the currentment of speeding up the improvement of air quality and governing the haze problem，this semi-dry desulfurization process has a very broad application prospects and promotion of significance.